It is because virtualbox versions <6.1.18 do not support kernel 5.11 Changelog:
https://www.virtualbox.org/wiki/Changelog VirtualBox 6.1.20 (released April 20 2021) Linux host and guest: Support kernel versions 5.11 (bug #20198) and 5.12 Bug: https://www.virtualbox.org/ticket/20198 ** Bug watch added: Virtualbox Trac #20198 http://www.virtualbox.org/ticket/20198 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1938953 Title: virtualbox-dkms 6.1.16-dfsg-6~ubuntu1.20.04.2: virtualbox kernel module failed to build To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/virtualbox/+bug/1938953/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
